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LM338: is Break when I attemp to get 1,5A using to basic configuration

gustavo adolfo
Prodigy 20 points
Part Number: LM338
Other Parts Discussed in Thread: LM138

The basic topology is described in the follow link:  "http://www.uni-kl.de/elektronik-lager/416059" 

Load Resistive = 14 ohms.

Vin = 20v

Vout = 15v

In the pass with the old device  this circuits worked correctly. Now, our company has tested to much but all have been burned . Is impossible get more than 1,2 Amperes .

I tried  improve the dissipation of the heat sink, with diodes suggested in the above link, capacitors etc.. but in all the cases this has been broken or result damaged .

I need to reach 4 amperes,

help!!

Best regards, 

  • 0
    TI__Mastermind 22610 points

    " ... with the old device  this circuits worked correctly ..."

    Old device? LM338 has not changed in 30 years, other than TI now owns the device.

    If possible please provide your schematic. The LM338 is relatively simple device.

    The link provided points to a National Semiconductor version of the LM138/LM338 datasheet, circa 1995.

          http://www.ti.com/lit/ds/symlink/lm338.pdf

    With Vin-Vout of 5V and 1A load current (Pd=5W) the package will get very warm and some heat-sink will be required. Attempting 4A (Pd=20W) will cause the package to become very hot, and robust heat-sinking, with air flow, will be mandatory.

    Due to the high power dissipation involved I would suggest that you consider a switch mode power supply.

  • 0 in reply to Donald Jones
    Prodigy 20 points

    Dear Donald,

    We have some devices that  work correctly and other of the same manufacture (National and ST microelectronics) that aren't working. We have also identified  that all device that do not work have a blue halo or circle in the pins (ajust & Vin ) and are lighter than the devices that work.

    We suspect that you changed the assembly factory, consequently this have been translated in possible quality problem. The devices that work correctly reach up to 4A (45° C in the heat sink) but the other devices just reach to the 1.5A and fail after that. 

    So,  I attach some photos of the devices under test, schematics and a photo  of our professional power supply that we have used for long time in our transmitters.

    Best Regards,

    Gustavo G.

    Chief Engineer C. Lensa

  • 0 in reply to gustavo adolfo
    TI__Mastermind 22610 points

    For the two photos of the eight TO-3 packages, those are all typical problematic devices?

    "We suspect that you changed the assembly factory, ... translated in possible quality problem ..."

    The National Semiconductor devices are 100% tested after assembly.

    Since this does not appear to be an Application issue, rather a Quality issue, please refer to the Customer Returns and Failure Analysis guidelines and process here:

    www.ti.com/.../resourceshome.page

  • 0 in reply to gustavo adolfo
    TI__Mastermind 22610 points

    Gustavo,

    We are checking now to see if any PCN has been issued approving any changes to the LM338K TO-3 package.

    As for issues with the ST version of LM338K, you will need to take that up with STMicroelectronics directly.

  • 0
    TI__Prodigy 330 points
    Verification of part authentication must be worked through your supply chain due to uncertainties regarding chain of custody of the products. Please be aware that the quality of the parts might be suspect if not received directly from TI or a TI authorized distributor. This can be due to decreased floor life (devices out of the moisture barrier bag), pre-usage of the parts, wrong storage procedures, mishandling, etc. TI strongly encourages you to purchase all your TI parts either directly from TI or from authorized TI distributors (focus.ti.com/.../distribcountryresults.jhtml).